Influence of dilution on arterial-phase artifacts and signal intensity on gadoxetic acid–enhanced liver MRI.
Sarah Poetter-Lang, Gregor O. Dovjak, Alina Messner, Raphael Ambros, Stephan H. Polanec, Pascal A. T. Baltzer, Antonia Kristic, Alexander Herold, Jacqueline C. Hodge, Michael Weber, Nina Bastati, Ahmed Ba-Ssalamah
European Radiology, volume 33, pages 523–534 (2023)
MRI with gadoxetic acid is widely and increasingly used to detect and characterize focal liver lesions. (1) However, one of the main limitations of gadoxetic acid is represented by arterial-phase (AP) artifacts: transient severe motion (TSM) and truncation artifacts. Both are due to the acute fleeting peak of gadoxetic acid blood plasma concentration, which causes acute transient dyspnea by activating central chemoreceptors, and the rapid disappearance of contrast from the imaging field. (2,3). The acute fleeting peak plasma gadoxetic acid concentration during the arterial phase can be prevented by saline dilution of gadoxetic acid at 1:1 and a slow injection rate of 1 ml/s (4), both off-label. The Authors’ aim was to assess the effect of these two strategies on AP artifacts reduction, on quantitative differences in signal intensity (SI), signal-to-norm, and contrast-to-norm, and hence focal lesion conspicuity on MR imaging.
This single-center retrospective study enrolled 112 patients who had undergone at least one non-diluted (ND) and one saline-diluted (D) gadoxetic acid–enhanced MRI at 1 ml/s for known or suspected liver or pancreaticobiliary diseases between December 2010 and July 2017. Patients who had undergone liver transplantation between the two MRIs or who had artifacts in all sequences were excluded.
Arterial-phase imaging was initiated at the individual patient’s t-peak, timed using a test bolus technique. Two blinded radiologists independently graded on a 5-point scale the presence of artifacts in dynamic T1-weighted sequences (unenhanced, arterial, portal venous, transitional, and 20-min HB phases). AP artifacts were defined as a score ≥ 4 in the arterial phase.(2) Then, quantitative signal intensity (SI) measurements were acquired by drawing regions of interest (ROI) at the level of the celiac trunk in five locations: aorta, portal vein, liver parenchyma, focal liver lesion, and paraspinal muscle in all phases in each patient. The SI value was normalized to the SI of the paraspinal muscle to obtain signal-to-norm ratio (SINorm). For focal lesions, the contrast-to-norm ratio (Cnorm) was also calculated.
AP artifacts were significantly reduced with dilution and were present in 35 (31%) of the non-diluted exams compared to 10 of the diluted exams (9%). An artifact severity score of 5 (i.e. nondiagnostic exam) was assigned to 18 exams (16%), 17 of which were in the non-diluted group. The scored severity of the artifacts was significantly higher in the ND compared to the D protocol (p < 0.001).
The mean absolute liver parenchyma SI and mean liver SINorm were significantly higher in the diluted exams in all contrast-enhanced phases. The mean SiNorm of the aorta in the AP and of the portal vein in the portal venous phase was significantly higher in the D exams (p = 0.005 and p = 0.035, respectively). There was no significant difference in the CNorm of all lesions (FNH, metastases, cirrhotic nodules, adenomas, hemangiomas) combined for D versus ND exams (all phases p > 0.05). Evaluation for lesion subtype, when n ≥ 10 (i.e., FNH and metastases), also revealed no significant difference in CNorm between the ND and D exams (all phases p > 0.05).
Arterial-phase artifacts did not have a significant influence on the SI of liver parenchyma on the ND (p=0.627) and on D (p=0.644) exams. The higher SI and SINorm in the diluted exams were attributed to contrast dilution and slower injection rate. In order to assess the effect of artifacts on lesion visibility, the authors also analyzed the detectability of lesions smaller than 1 cm. They were able to detect 5 more lesions and to see 3 lesions better on the diluted vs non-diluted scans. They attributed these findings to TSM artifact reduction as truncation artifacts did not influence the visibility of these lesions.
The high relaxivity of gadoxetic acid explains why the difference in SI and SINorm was largest in the HBP. Also, during recirculation, on the diluted exams hepatocyte transporters had more time to accumulate gadoxetic acid due to doubling the volume on the diluted exams.
The Authors acknowledge some limitations. First, the retrospective study design, with a relatively small cohort and few comparable lesions, as the majority of the patients with HCC and metastases underwent treatment leading to a change in the appearance of these lesions between ND and D exams. Notwithstanding these limitations, the authors obtained significant results. A prospective study, ideally in a larger cohort, is warranted to confirm the findings of the study. Furthermore, a test bolus injection was used to estimate peak enhancement, which may affect subsequent signal intensity, choosing the same delay. This problem was overcome by the choice of intraindividual comparison for measuring SINorm differences on D versus ND exams. In this way, they also eliminated the influence of factors that can contribute to severe AP artifacts such as gender, weight, and BMI.
In conclusion, the authors demonstrated that 1:1 saline dilution of gadoxetic acid, administered at the slower injection rate of 1 ml/ s via a power injector, reduces significantly arterial phase transient severe motion artifacts, while increasing normalized signal intensity and preserving lesion contrast compared to standard non-diluted images.
References:
- Ba-Ssalamah A, Uffmann M, Saini S, Bastati N, Herold C, Schima W (2009) Clinical value of MRI liver-specific contrast agents: a tailored examination for a confident non-invasive diagnosis of focal liver lesions. Eur Radiol 19:342–357
- Davenport MS, Bashir MR, Pietryga JA, Weber JT, Khalatbari S, Hussain HK (2014) Dose-toxicity relationship of gadoxetate disodium and transient severe respiratory motion artifact. AJR Am J Roentgenol 203:796–802
- Huang SY, Seethamraju RT, Patel P, Hahn PF, Kirsch JE, Guimaraes AR (2015) Body MR imaging: artifacts, k-space, and solutions. Radiographics 35:1439–1460
- Kim YK, Lin WC, Sung K et al (2017) Reducing artifacts during arterial phase of gadoxetate disodium-enhanced MR imaging: dilution method versus reduced injection rate. Radiology 283:429–437
- Jornada Tda S, Murata CH, Medeiros RB (2016) Influence of partial k-space filling on the quality of magnetic resonance images. Radiol Bras 49:158–164
Giulia Tomelleri is a third-year radiology resident at the Radiology Department of the University of Verona, Italy. She graduated in 2020 in Medicine and Surgery at the University of Ferrara. Her main field of interest in diagnostic imaging is Abdominal imaging, with focus on gastrointestinal and hepato-pancreato-biliary disease.
Comments may be sent to: giulia.tom94(at)gmail.com
